Simultaneous magnesium precipitation and lithium enrichment with extreme separation factor for high Mg/Li ratio brines

Lithium and its compounds are critical strategic resources with wide-ranging applications. This study developed a bipolar membrane precipitation coupled electrodialysis enrichment (BMp-EDe) process for extracting lithium from brines with an Mg/Li ratio of 20. The method is based on phase separation achieved through precipitation-coupled ion permeation and a synergistic mechanism for ion enrichment, resulting in significant process intensification. Key factors such as current density, molar ratio between diluate and base chambers, and base chamber concentration were optimized to control nucleation and prevent membrane fouling. Under conditions of current density ranging from 200 to 400 A·m −2 and a molar ratio of the diluate chamber to the base chamber between 13 and 16, the magnesium removal rate in the BMp-EDe process is found to exceed 99.90 %, with a separation factor greater than 20,000. The optimal separation factor is observed to reach 40,244, with a magnesium removal rate as 99.96 % and a lithium recovery rate as 95.32 %. With optimized operation conditions, the energy consumption of magnesium precipitation decreased from 11.89 kWh·kg −1 (Mg 2+ ) to 7.97 kWh·kg −1 (Mg 2+ ). Thus, an alternative method is presented that employs commercial bipolar membranes to achieve ultra-high magnesium‑lithium separation efficiency. Additionally, a mechanism for the continuous operation of the magnesium precipitation chamber is validated, which can effectively prevent membrane fouling.